1. Field of the Invention
The present invention relates to a vehicular switch particularly having a pivoting knob of, for example, a lever switch of a combination switch installed at a steering column of a vehicle or the like.
2. Description of Related Art
In a lever switch of a combination switch or the like of a vehicle, a lever per se is used as an operating portion of a turn signal switch or a passing switch and is also used as a dimmer switch by providing a pivoting knob at the lever or for controlling a wiper speed.
FIG. 4 is a sectional view showing a structure of a front end portion of a lever switch having a middle pivoting knob at a middle portion for controlling a wiper speed for, for example, controlling intermittent time in an intermittent mode of the wiper including a surrounding of the middle pivoting knob in the lever.
In a lever 10′, a shaft portion 12 is extended from a lever main body portion 11′ to a front end thereof and a front end fixing block 20 and a middle fixing block 30 are respectively provided at a front end and a middle of the shaft portion 12. Between the middle fixing block 30 and the lever main body portion 11′, a middle pivoting knob 40′ for controlling the wiper speed is pivotably provided around the shaft portion 12.
The middle pivoting knob 40′ comprises an operating ring portion 41, both ends of which are in an axial direction and are supported by an end edge on a side of a lever main body of the middle fixing block 30 and an end edge of the lever main body portion 11′ and a movable contact holding block 42′ on an inner side thereof. The movable contact holding block 42′ is extended from a side edge on a side of the lever main body portion 11′ into the lever main body portion by a predetermined length and is provided with a movable contact 43 at an end face thereof.
A fixed contact plate 50′ is fixed at the lever main body portion 11′ to be opposed to the movable contact 43 of the movable contact holding block 42′.
The movable contact holding block 42′ is further provided with a ball hole 46 opened to a side of the middle fixing block 30, holds a ball 48 urged by a spring 47 and presses the ball 48 to a cam 31 provided at the middle fixing block 30.
As shown by FIG. 5, the fixed contact plate 50′ is provided with a resistor 52 in a circular arc shape and conductors 54 and 55 extended from both ends thereof on a plate face thereof. Further, the resistor 52 and the conductors 54 and 55 constitute a ring-like shape as a whole and terminals 56 and 57 at both ends thereof are connected to lead wires (not illustrated).
The resistor 52 is formed by coating a paste comprising a mixing agent of resin and carbon.
The movable contact 43 includes an arm extended in a circular arc shape and is arranged such that one end thereof slides on the resistor 52 of the fixed contact plate 50 and the other end thereof slides on the conductor 54.
Thereby, when the intermediate pivoting knob 40′ is pivoted, a position of the arm of the movable contact 43 on the resistor 52 is changed and a resistance value between the terminals 56 and 57 of the fixed contact plate is changed.
A front end portion of the lever 10′ is also provided with a front end pivoting knob 70 attached to a pivoting block 60 between the front end fixing block 20 and the middle fixing block 30 and a fixed contact plate 75 and the pivoting block 60 is provided with a movable contact.
Meanwhile, according to the conventional lever switch having the above-described constitution, depending on conditions, there poses a problem that when a passenger charged with static electricity touches a vicinity of the middle pivoting knob 40 for operation, the static electricity is applied to the resistor 52 of the fixed contact plate 50′ and the resistor 52 is damaged.
For example, static electricity applied to a vicinity of an end portion B of the middle pivoting knob 40 propagates in air having small resistance and escapes to the fixed contact plate 50′ by passing a gap between the middle pivoting knob 40′ and the lever main body portion 11′.
At this occasion, when the static electricity is applied to a central position in a peripheral direction of the resistor 52 of the fixed contact plate 50′, the resistance of the resistor 52 is maximized against the static electricity escaping to the conductors 54 and 55 at the both ends, heat is generated and a resin component of the resistor 52 is burnt.
Therefore, although a variable range of the resistance value by the resistor 52 is set to, for example, 0Ω through 1 kΩ, the variable range is changed to 0Ω through 700Ω and operation of the wiper set to predetermined minimum speed cannot be carried out and a drawback that the wiper cannot be used at fast speed is brought about.
In order to avoid such a phenomenon, it is necessary to increase a distance d from-an end edge of the lever main body portion 11′ to the fixed contact plate 50′, shown in FIG. 4, as large as possible.
However, when the distance d is increased, a degree of freedom of the shape of the lever is lost, and the distance d cannot sufficiently be ensured in relation with arrangement of an inner structure.
When a resistor is also provided at the fixed contact plate 75 for the front end pivoting knob 70, a similar problem occurs.